The present invention relates to battery packs and a method for constructing the same.
Referring to FIG. 3, battery pack 10 typically has rechargeable cells 11 connected in series and/or parallel via connectors, such as metal straps 13. The cells 11 may be held together by a plenum or plate 12. The straps 13 may be disposed between the plate 12 and cells 11. Alternatively, plate 12 may be disposed between cells 11 and straps 13, whereas the straps 13 contact the cells 11 through holes in plate 12.
This assembly is then disposed in a housing 15. Cables or wires connected to cells 11 may extend into a terminal block 14, which allows the battery pack 10 to be connected to electric and/or electronic devices such as power tools, chargers, cellular telephones, etc.
Referring to FIGS. 1 and 3, typical cells 11 include cells produced by Sanyo Energy, such as model no. N2400. Such cells 11 may have weld area 11W, where the negative collector inside the cell is welded to the exterior can during the production of cell 11. This process may be done from the outside of the cell 11 using a laser. After the weld is completed, a weld area 11W having a diameter of about 4 or 5 millimeters is left. This weld area 11W may be sensitive to exterior pressure, heat, and electrical current.
During the construction of battery pack 10, cells 11 are typically welded together using double protrusion nickel straps 13, which have protrusions 13P. During the welding process, a strap electrode 16S is disposed on strap 13 while cell electrode 16 contacts the cell 11 directly. Current is passed through strap electrode 16S, strap 13 and out the cell 11 into cell electrode 16C, resulting in heat and finally welding.
This is problematic because cell electrode 16C partially or completely contacts weld area 11W of cell 11. This welding process may result in early cell failure.